The objective of this research is to characterize the viral and host proteins involved in cellular transformation by Rous sarcoma virus. Genetic studies have shown that the genome of Rous sarcoma virus contains a region which is responsible for the maintenance of the transformed state. This segment of the genome is deleted in transformation-defective mutants which are usable to transform fibroblasts in vitro or produce sarcomas in vivo. Mutants which are temperature-sensitive in their ability to transform have also been isolated: cells infected by these mutants are transformed at the permissive temperature, but revert to a phenotypically normal state when shifted to the non-permissive temperature. A two-dimensional gel electrophoresis technique will be used to study the pattern of protein synthesis in virus-infected cells. In this technique complex protein mixtures are resolved first by isoelectric focusing and then in a second dimension by electrophoresis in the presence of sodium dodecyl sulfate. The pattern of protein synthesis in cells infected by wild type virus and various viral mutants will be examined, in order to identify virus-specific proteins involved in viral replication and transformation. The effects of temperature shifts on the pattern of host protein synthesis in cells infected by temperature-sensitive mutants will also be examined.